When we talk about light, we usually mean the light that we can see with our eyes.
This type of light is called visible or optical light.
Light is one way that energy can be transferred. This means it can move from one place to another.
Most of the light that reaches Earth comes from the Sun.
The energy carried by sunlight makes it possible for life to survive on Earth.
- Luminous and Non-Luminous Objects
There are other sources of light on Earth, such as fire and lightbulbs. Lightbulbs use electricity or solar power, and some of that energy is released as visible light.
Objects that create their own light are called luminous objects.
Other objects do not produce light themselves. Instead, they reflect light that falls on them. Examples include books, clothing, and the Moon.
These are known as non-luminous objects.
- How does light travel?
For us to see something, light must travel from a source to our eyes. On Earth, light usually travels in straight lines.
A ray diagram is used to show the path that light takes as it travels.
It can also show what happens when light reaches a surface, such as a lens, mirror, or other object.
In ray diagrams, light is shown using straight lines. Arrows are added to show the direction the light is moving.
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CreditThis work by The Schools' Observatory is licensed under All rights reservedA ray diagram showing light (represented by the red arrows) emitted from a bulb Anything placed in the path of light will affect what we see.
A window is transparent. This means that light can pass straight through it.
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CreditThis work by The Schools' Observatory is licensed under All rights reservedLight (represented by the red arrows) passing through a transparent object. An opaque object, such as a ball, blocks light. This creates a shadow.
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CreditThis work by The Schools' Observatory is licensed under All rights reservedLight (represented by the red arrows) blocked by an opaque object, creating a shadow. Some of the blocked light is absorbed by the object, which can make it warmer. The rest of the light is reflected.
This reflection is how we see objects.
Light hits an object and bounces off its surface, travelling to our eyes.
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CreditThis work by The Schools' Observatory is licensed under All rights reservedLight (represented by the red arrows) reflecting off a book and reaching our eyes. Some objects reflect more light than others. Very reflective objects, such as mirrors, can change the direction of light. This is how most telescopes work.
- Colours of Light
The light we see often appears white, but it is made up of every colour of the rainbow.
White light can be split into its colours using a glass prism. This also happens naturally when sunlight passes through rain to create a rainbow.
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CreditThis work by Jibin 1840404 is licensed under Creative Commons Attribution Share Alike 4.0 InternationalImage
CreditThis work by SharkD is licensed under Creative Commons Zero v1.0 UniversalHow the primary colours of light combine The three primary colours of light are red, green, and blue.
Our eyes contain special cells called cones that detect colour. We have three types of cones, one for each primary colour.
When more than one type of cone is used, the colours combine.
These combinations create all the colours we can see.
An object’s colour depends on the light it reflects. White objects reflect all colours, while perfectly black objects reflect none.
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CreditThis work by The Schools' Observatory is licensed under All rights reservedWhite and black surfaces reflecting different amounts of light If an object appears green, it is reflecting green light and absorbing the other colours.
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CreditThis work by The Schools' Observatory is licensed under All rights reservedLight is more complex than this. Beyond visible light, there are many other types of light. Together, these make up the electromagnetic spectrum.